Continuous method of making porous strip material



May 15, 1956 J, B BRENNAN 2,745,141

CONTINUOUS METHOD OF MAKING POROUS STRIP MATERIAL Filed Nov. 24 1952 UnitedStates Patent() CONTINUOUS METHOD OF MAKING POROUS STRIP MATERIAL Joseph B. Brennan, Cleveland, Ohio Application November 24, 1952, Serial No. 322,276

6 Claims. (Cl. 18-57) This invention relatesy toporous dielectric strip material suitable for use in electrolytic devices and the continuous method of making same.

This application is a continuation-impart of my copending application Serial No. 69,863, tiled January 8, 1949, now abandoned.

The preferred method of making spacers according to this invention is to spray deposit particulate, dielectric material such as thermoplastic material, for example polyethylene, through a heat zone whereby the exterior only of the particles becomes molten as particles travel through a heat zone and prior to their deposition on a constant speed moving base.

The moving base on which the exteriorly molten particles are .deposited is maintained at a temperature lower than the melting point of the dielectric material being sprayed.

The spray of particulate thermoplastic lparticles can be produced, for example, by the use of a Schori, or

equivalent spray gun maintained at constant operating conditions by maintaining constant gas pressures so that the particles are projected .from the nozzle of the` spray gun at a constant quantity rate. p

The temperature of the ame associated with the-spray gun is so regulated that the thermoplastic particles pass through this flame the exterior of these particles only, becomes melted and when the particles are deposited on to the constant speed base due to the lower temperature of the base they are immediately chilled and solidied as they form a continuous layer on the constantly moving base.

The rate of feed of the particulate spray and the particulate density of this spray are maintained at constant rate so that the particles agglomerate in thin layer form and knit together to form a continuous, porous vsheet which is, according to this invention, solidified on the constantly moving base due to the lower temperature thereof and constantly stripped from the moving base in continuous sheet form for further processing and use. If preferred, a thin porous base material such as paper may be used as a base for layer deposition of the spray deposited exteriorly molten particl so that 'a composite layer results and may be rremoved from the constantly moving base as a composite material. A v

Other fibrous material such as, for example, parallel cords or ilaments, or yarns, or gauze may be used as a base for making composite material.

In any case, according to this inventionthe spray deposited particles are solid when spray deposited except for their exterior skin or surface which is molten.`

The exteriorly molten dielectric material particles, when sprayed at a constant rate according *to this in-V vention, on to the constantly moving base, vare chilled upon deposition and are coherently attached instrip layer form so that interparticulate interstitial channels, or pores extend through the strip ylayerfrom face to face and from edge to edge so that, for example, electrolytes such as those used in storage batteries, or eleoice trolytic condensers will readily pass through the orifices or pores in the strip, or sheet of dielectric particulate material made according to this invention.

In any case according to this invention the welded particles are in porous layer form having theainter-particle interstices extending from face to face. The walls of the interstitial pores are comprised of exterior particle surfaces. The layer of particles is a continuous network, or lattice-work in layer form.

The electrolytic spacers made according to this invention may be spaced to act als-retainers, for instance, for the active material formed on orspread on a porous electrode storage battery plate such as is described in my co-pending U. S. patent application Serial No. 41,699, now abandoned.

It is preferred according to my invention' that this spacer be relatively incompressible so that the poresv thereof are not closed up,fwhen compressed, in association with the battery plates.

It is also contemplated according to my invention that this porousdielectric electrolytic spacer may be made to conform to the exterior shape of the, for instance, battery plates associated therewith so that, for instance, two of these spacers can be placed around abattery plate tightly sothat the edges of the spacers can be cemented together so as to. form a porous envelope as well as a structural reinforcement and retainer for the active battery plate. This'will prevent disintegration of battery plates, which is one of the 'principlediiiiculties now encountered in prolonging the life of present day alkaline or acid batteries.

Heretofore in the battery industry, the mechanical retension of the active elements in place has been principally dependent upon the structural strength of the plate or electrode itself. Accordin'gto my invention a mechanically strong porous spacer can be used as a support for a battery plate and the active material associated therewith.. l 1

If desired, the plastic separator may be extended up over the normal level of electrolyte in the` electrolytic cell and made to` support substantially the terminal members of the electrolytic cell and thus enable one to use less metal in the terminal members of y'the electrolytic According to this invention and by way of example,

a cloud of dielectric particles such as particles of polystyrene'of say 60 to 150 mesh may be continuously projected in a gas stream through a ame'preferably non-oxidizing, with temperature of llame SGO degrees to 1300 degrees F., onto a temperaturecontrolled, con-l 'i tinuously moving polished metallic base s that the par; v' ticles'are exteriorly only heatedl to a molten condition in transit and when they light on the preferably iiuid cooled moving metallic .base they arel immediately chilled -to solid condition after attaching themselves at spaced points on' their surfaces to adjacent particles. l A line mesh metallic screen may be substituted for the polished metallic constantly moving base if preferred. This screen may, for example, be made of mesh stainless steel woven wires.

As stated above, paper or other fibrous material may also be used as a base on which to deposit the porous dielectric, exteriorly molten particles in layer form to make-composite sheetmaterial according to this invention.

In the accompanying sheet of drawings forming a part of this specification:

Fig. l is an elevational` View of a diagrammatic form illustrating the method of this invention;

Fig. 2 is a transverse section on a larger scale taken through the sheet material being produced, as indicated by section line 2-2 of Fig. 1;

Fig. 3 is an elevational View similar to Fig. 1 but showing the use of a web of porous base material in carrying out the method; and

Fig. 4 is a transverse section on a larger scale taken through` the composite sheet material on section line 4-4 of Fig. 3.

Referring further to Fig. l of the drawing for explanation, l illustrates a plastic powder spray or projecting device which will cause plastic particles exteriorly, only to become molten to deposit in a continuous layer 2 immediately cooled to solid after or upon deposition. 5 illustrates a stripper knife or device to assist in removing the :so-deposited porous layer 2 from the drum 3 whereupon said porous strip may be woundy into a roll on the clutch driven roll 7 which rotate on the shaft 8 at constant speed. 6 illustrates a lubricator and polisher as of felt to keep the surface of the drum 3 slick. 4 illustrates hollow shaft or drum 3 for introduction of fluid coolant therein.

The rate of feed of the plastic powder must be constant and proportioned to secure the desired thickness of spray deposited layer.

A vibrating screen dropping the plastic particles through a heat zone may be used also to deposit the plastic particles on the moving drum.

In any case the object of this invention is to produce an interparticle porosity in a continuously produced layer of plastic particles welded together at spaced points in their adjacent surfaces so as to form a continuous flexible porous sheet which has interstitial pores running in all and random directions forming channels which extend from one surface to another at least and to continuously remove the so produced layer.

Fig. 2 illustrates a cross-section of the layer 2 so produced. 1.0 illustrates theparticles comprised in such a sheet and 11 illustrates the point of Weld theretbetween and 9 illustrates the openings or irregular channels extending therethrough.

In any case, according to my invention I make a porous thin layer comprising solid dielectric particles heat welded to adjacent particles at spaced points on their surfaces having interfacial pores extending therethrough. No solvent is needed according to my invention to effect atomization and weldability of these particles.

In any case, my invention comprises the continuous deposition of a layer of only exteriorly molten, plastic dielectric particles and fast chilling of said layer to prevent tlow of the molten portions to prevent the production of an impervious sheet such as would be had if chilling were not effected after deposition.

The chilling may be effected or assisted also by a coolant propelled by fans or pumps and directed at the layer immediately after deposition.

In spray depositing according to my invention the plasvtic particles are .fed with a screw or other constant supply measuring means in order to get constant density of particles in the spray field and in order to deposit a layer of uniform thickness.

This can be done by a hopper belt and doctor blade or a screw feed and doctor blade or other means so long as rate of feed and distribution are constant for a given thickness of strip material to be produced. Such feed or distribution devices must be coordinated with the speed of the moving base onto which deposition or/and distribution is made.

In spray depositing the externally molten particles to form a porous layer of uniform thickness the particle density of the spray must be uniform as can be done with a vibrating screen over the moving surface or the sprays if of non uniform density throughout their core-shaped patterns can be overlapped to secure uniform thickness or the spray patterns can be made uniform by causing thin depositions to overlap by multiple continuous spraying so that the thin portions which overlap are substantially equal in thickness to the non-overlapped thick portions.

Dielectric porous strips made according to my invention are suitable for use in electrolytic cells as separators. The materials should be selected so as to be non-reactive with the electrolytes and other components involved.

I have found that by spray depositing only superiicially melted particles of fuseable material such as of metal continuously to produce porous strip material that added porosity in strip material is attainable over strip material produced by spray depositing completely molten particles. This is because quicker cooling is attainable and less distortion of the particles on impact is attainable and the particles retain their shape on deposition.

This is true in making strip material of metal particles for storage batteries and for metallic iilter membranes and for electrolytic condenser electrodes. Greater exposed interparticulate area remains for electrolyte contact when aluminum, or other film forming metallic particles are only exteriorilly and superlicially fused on spray deposition. Thus for a given weight of metal particles such as aluminum when spray deposited with only the exterior of the particles melted prior to and during deposition I secure 50 to 100% more capacity in a porous particulate anode strip made therefrom as I secure from an anode of the same weight made from completely melted spray deposted aluminum particles.

It is also observed by me that when I spray deposit exteriorly molten dielectric particles interiorly solid I get an increased porosity in a given size sheet under the procedure of this invention over that attainable by spray depositing completely molten particles.

Regulation of porosity is possible in ion exchange membranes and osmotic membranes made according to this invention by regulating the particle sizes chosen for the spray deposition but in any case heat suicient only for supercial melting of the particles is applied.

I tind that satisfactory particle size, for example, is from 2-8 microns either of metal for porous conductive electrodes or for dielectric sheet material according to this invention. The ame temperature must be sufficient in all cases to melt the outer Surface of the particles being sprayed and the time of exposure of the particles to the flame must be less than that required to completely melt the particles being sprayed. The more uniform the particle size the more uniform porosity and area of the resulting strip produced according to this invention.

Fig. 3 of the drawing shows the method of this invention being carried out in the same manner as has already been described above, but in which the sprayed particles lti are deposited on a web 12 of relatively thin porous tiexible base material, such as the above-mentioned porous paper base, instead of being deposited directly on the drum 3. The porous base material 12 is here shown as a strip being Withdrawn from a roll 13 of that material and being led over the cooling drum 3. The strip 12 and the deposited particles Iii forming the porous adherent layer 2 thereon, constitute a composite porous sheet material 14 which is wound on the roll 15 as the composite material is produced. When the method is carried out with the use of the base strip i2, the stripping knife S and the polisher 6 can be omitted if desired.

Having described my invention, what I claim is:

1. In a method of making porous flexible dielectric sheet material the steps of, creating a spray iield of interiorly solid and exteriorly molten dielectric particles, causing relative traversing movement between said spray iield and a base, depositing a layer of said particles on the base with the exteriorly molten portions of adjacent deposited particles in fused engagement with each other at spaced points of their surfaces and with interstices re- 5 maining between said adjacent particles soA that the deposited and fused particles constitute such dielectric sheet material which is rendered porous by the presence of said interstices, `and stripping said sheet material from said base.

2. In a method of making porous exible dielectric sheet material the steps of, creating a spray eld of interiorly solid and exteriorly molten dielectric particles, causing relative traversing movement between said spray eld and a heat conducting base, depositing a layer of said particles on the base with the exteriorlymolten portions of adjacent deposited particles in fused engagement with each other at spaced points thereof and with interstices remaining between said adjacent particles so that the deposited and fused particles constitute such dielectric sheet material which is rendered porous by the presence of said interstices, cooling and solidifyingsaid deposited particles in said fused engagement by the removal of heat through said base, and stripping said sheet material from said base.

3. In a method of making composite porous flexible dielectric sheet material the steps of, advancing a web of thin porous flexible base material over a support, creating a spray eld of interiorly solid and exteriorly molten dielectric particles and directing the spray ield toward said base material, and depositing a layer of said particles on lsaid base material with the exterior-ly molten portions of adjacent deposited particles in fused engagement with each other at spaced points of their surfaces and with interstices remaining between said adjacent particles so that said base material and the deposited and fused particles constitute said composite porous flexible sheet material, and leading the composite sheet material away from said support.

4. A method as dened in claim 3 and which also includes the .steps of, leading the base material over a continuously moving support while said layer 0f dielectric particles is being deposited on said base material, cooling said support, and stripping the composite sheet material from said support.

5. A method as defined in claim 3 in which said base material comprises parallel filaments.y y

6. A method as defined in claim 3 in which said base material comprises gauze.

Macht et a1 Oct. 29, 1946 Manning Mar. 9, k1948 

1. IN A METHOD OF MAKING POROUS FLEXIBLE DIELECTRIC SHEET MATERIAL THE STEPS OF, CREATING A SPRAY FIELD OF INTERIORLY SOLID AND EXTERIORLY MOLTEN DIELECTRIC PARTICLES, CAUSING RELATIVE TRANSVERSELY MOVEMENT BETWEEN SAID SPRAY FIELD AND A BASE, DEPOSITING A LAYER OF SAID PARTICLES ON THE BASE WITH THE EXTERIORLY MOLTEN PORTIONS OF ADJACENT DEPOSITED PARTICLES IN FUSED ENGAGEMENT WITH EACH OTHER AT SPACED POINTS OF THEIR SURFACES AND WITH INTERSTICES REMAINING BETWEEN SAID ADJACENT PARTICLES SO THAT THE DEPOSITED AND FUSED PARTICLES CONSTITUTE SUCH DIELECTRIC SHEET MATERIAL WHICH IS RENDERED POROUS BY THE PRESENCE OF SAID INTERSTICES, AND STRIPPING SAID SHEET MATERIAL FROM SAID BASE. 